1. Field of the Invention
The present invention relates generally to the field of disc drive storage, and more particularly to multilayer perpendicular magnetic media.
2. Description of the Related Art
Conventional disc drives are used to magnetically record, store and retrieve digital data. Data is recorded to and retrieved from one or more discs that are rotated at more than one thousand revolutions per minute (rpm) by a motor. The data is recorded and retrieved from the discs by an array of vertically aligned read/write head assemblies, which are controllably moved from data track to data track by an actuator assembly.
The three major components making up a conventional hard disc drive are magnetic media, read/write head assemblies and motors. Magnetic media, which is used as a medium to magnetically store digital data, typically includes a layered structure, of which at least one of the layers is made of a magnetic material, such as CoCrPtB, having high coercivity and high remnant moment. The read/write head assemblies typically include a read sensor and a writing coil carried on an air bearing slider attached to an actuator. This slider acts in a cooperative hydrodynamic relationship with a thin layer of air dragged along by the spinning discs to fly the head assembly in a closely spaced relationship to the disc surface. The actuator is used to move the heads from track to track and is of the type usually referred to as a rotary voice coil actuator. A typical rotary voice coil actuator consists of a pivot shaft fixedly attached to the disc drive housing closely adjacent to the outer diameter of the discs. Motors, which are used to spin the magnetic media at rates of higher than 1,000 revolutions per minute (rpm), typically include brushless direct current (DC) motors. The structure of disc drives is well known.
Magnetic media can be locally magnetized by a read/write head, which creates a highly concentrated magnetic field that alternates direction based upon bits of the information being stored. The highly concentrated localized magnetic field produced by the read/write head magnetizes the grains of the magnetic media at that location, provided the magnetic field is greater than the coercivity of the magnetic media. The grains retain a remnant magnetization after the magnetic field is removed, which points in the same direction of the magnetic field. A read/write head that produces an electrical response to a magnetic signal can then read the magnetization of the magnetic media.
Magnetic media structures are typically made to include a series of thin films deposited on top of aluminum substrates, ceramic substrates or glass substrates. FIG. 1 illustrates a conventional magnetic media structure having a substrate 110, a first layer 112 made of CoFeB, a second layer 114 made of Ta or TaOx, a third layer 116 made of CoFeB, a fourth layer 118 made of Ta or TaOx, a fifth layer 120 made of CoFeB, a sixth layer 122 made of Ta or TaOx, a seventh layer 124 made of CoFeB, an eighth layer 126 made of Ta, a ninth layer 128 made of Indium Tin Oxide (ITO), a tenth layer 130 made of CoCrRu, an eleventh layer 132 made of boron-oxide (BOz), a twelfth layer 134 made of B, a thirteenth layer 136 made of nineteen bi-layers having CoCr/Pd, and a fourteenth layer 138 made of hydrogenated and/or nitrogenated carbon (CHN).
Substrate 110 is typically made of Aluminum (Al), nickel-phosphorus plated aluminum, glass or ceramic. Although all of the layers contribute to the magnetic properties of the stack, the thirteenth layer 136, which is made out of the nineteen bi-layers CoCr/Pd, plays an important role in making a magnetic media stack with desirable magnetic recording properties.
The magnetic media structure described with reference to FIG. 1 above is made using conventional magnetic media manufacturing processes. Conventional media manufacturing processes include texturing substrate 110, cleaning substrate 110, and depositing layers 112 through 138. The deposition process includes sputtering target material of usually the same material as their respective layers so that thin films of the sputtered material grow on the substrate. The deposition process is usually done at ambient temperatures and only after the deposition chamber has been evacuated to low pressures. Multilayer perpendicular media is typically deposited under ambient temperature for sharp interfaces between Co and Pd/Pt layers.
The magnetic layers of the alloy perpendicular or longitudinal recording media, which include a single or a couple of magnetic layers wherein the thickness of each layer can range from about 10 Å to about several hundred angstroms, are typically deposited onto substrates that have been heated to high temperatures, such as 250° C. Growing thin films on hot substrates reduces noise by promoting desired crystallographic orientations and by enhancing Cr segregation into grain boundaries. During deposition, the higher substrate temperature enhances molecule mobility permitting desired crystallographic orientations to grow and enhancing Cr segregation into grain boundaries reduces exchange coupling of the grains reducing noise.
The magnetic media structure of FIG. 1 lacks optimal magnetic properties because of high noise resulting from high magnetic exchange coupling between grains. The requirement to have sharp interfaces between different layers while having a laminated alternative thin layer structure consisting of Co-alloy and Pd or Pt that is different from conventional alloy media, makes it desirable to find ways to reduce the exchange coupling of multilayer perpendicular media and maintain sharp interfaces between Co-alloy and Pd or Pt films. This is especially true for the media deposited at ambient temperature. Therefore what is needed is a magnetic media structure with high magnetic anisotropy of the multilayer media, sharp interfaces between the Co-alloy films and the Pd or Pt films that reduces noise that can be deposited at ambient temperatures.